This invention relates to an electronic musical instrument, and more particularly, to a system of generating basic tone source waveshapes having frequencies corresponding to respective keys of the musical instrument by utilizing a digital circuit.
A conventional apparatus for generating a musical tone waveshape comprises a memory device which stores a particular musical tone waveshape and means for reading out the stored waveshape at selected rates for producing respective musical tone waveshape signals. However, in order to produce signals of various musical tone waveshapes it is necessary to provide a plurality of memory devices because it is necessary to use one memory device for each tone waveshape. In addition, the prior art apparatus cannot accurately form tone signals of any desired waveforms. According to one type of prior art musical tone waveshape generating system, a fundamental wave and sinusoidal waves corresponding to respective higher harmonics are read out from a memory device in which a sinusoidal wave is stored and the read out fundamental and harmonic waves are compounded at suitable level ratios to form a musical tone signal of any desired waveshape. However, these prior art systems require a number of complicated circuit components such as a plurality of tone memories, memory read out devices and wave compounding devices. Thus, not only is the circuit construction extremely complicated and expensive but also it is necessary to use considerably high operating frequencies.